On Sat, Apr 27, 2019 at 03:38:44PM +0200, Greg KH wrote: > On Fri, Apr 26, 2019 at 03:04:29PM -0400, Joel Fernandes (Google) wrote: > > Introduce in-kernel headers which are made available as an archive > > through proc (/proc/kheaders.tar.xz file). This archive makes it > > possible to run eBPF and other tracing programs that need to extend the > > kernel for tracing purposes without any dependency on the file system > > having headers. > > > > A github PR is sent for the corresponding BCC patch at: > > https://github.com/iovisor/bcc/pull/2312 > > > > On Android and embedded systems, it is common to switch kernels but not > > have kernel headers available on the file system. Further once a > > different kernel is booted, any headers stored on the file system will > > no longer be useful. This is an issue even well known to distros. > > By storing the headers as a compressed archive within the kernel, we can > > avoid these issues that have been a hindrance for a long time. > > > > The best way to use this feature is by building it in. Several users > > have a need for this, when they switch debug kernels, they do not want to > > update the filesystem or worry about it where to store the headers on > > it. However, the feature is also buildable as a module in case the user > > desires it not being part of the kernel image. This makes it possible to > > load and unload the headers from memory on demand. A tracing program can > > load the module, do its operations, and then unload the module to save > > kernel memory. The total memory needed is 3.3MB. > > > > By having the archive available at a fixed location independent of > > filesystem dependencies and conventions, all debugging tools can > > directly refer to the fixed location for the archive, without concerning > > with where the headers on a typical filesystem which significantly > > simplifies tooling that needs kernel headers. > > > > The code to read the headers is based on /proc/config.gz code and uses > > the same technique to embed the headers. > > > > Other approaches were discussed such as having an in-memory mountable > > filesystem, but that has drawbacks such as requiring an in-kernel xz > > decompressor which we don't have today, and requiring usage of 42 MB of > > kernel memory to host the decompressed headers at anytime. Also this > > approach is simpler than such approaches. > > > > Reviewed-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Thanks for the Reviewed-by tag. I believe there are still 2 logistical things to merge this. 1. Location of the header archive: Olof and Steve did not like it to be in /proc and instead /sys seemed a better choice they are Ok with. Me and Greg were Ok with it being in /sys/kernel/. Alexei, Greg and me are Ok with either proc or Sys. 2. Who is going to pull this patch: This seems a matter of where the header archive resides. If it is in /sys/kernel/ then I am assuming Greg will pull it. Masahiro has given his Reviewed-by tag, is he the one to pull it? Let us agree on these open questions so I can respin the patch to be based on that and move this forward. thanks! - Joel
